Field of the Invention
The present invention relates to an image reading apparatus, more particularly, to apparatuses that illuminate a surface of an original and read an image according to a line-sequential scheme; the apparatuses include image scanners, copiers, and facsimiles.
Description of the Related Art
Conventionally, a light illuminating device (an original illuminating device) used in an image reading apparatus, such as an image scanner, which illuminates a surface of an original and reads an image according to the line-sequential scheme, guides light from a light source to the surface to be illuminated, and thus illuminates a reading target area (reading line) at a desired illumination intensity. Accordingly, a read image with a low noise is obtained.
Known line-sequential schemes for reading include a scheme of reading an original placed on what is called platen glass while moving a reading unit, and a scheme of reading through a fixed reading unit while moving an original (hereinafter, called feeding-reading). A mechanism called an ADF (Auto Sheet Feeder) or a sheet feed is used for feeding-reading.
In general, in the case of copying a large amount of originals at high speed, the originals are conveyed at high speed while being read. To read the original moving at high speed, the accumulation time at a light receiving element is required to be set short with respect to the speed for feeding the original. To reduce increase in noise according to this setting, a bright F-number is required to be adopted for the reading optical system, or the number or output of light sources is required to be increased, for example.
However, such a configuration is an overdesigned one for a fixed original reading mode. In the fixed original reading mode, the original is replaced for each time of reading. Improvement in speed is not so effective in such situations.
Here, according to Japanese Patent Application Laid-Open No. 2013-236286, a configuration is known where double-structured reflection plates (a first and a second reflection plate) are provided in the clearance between a light source unit and a platen, to increase the amount of illumination onto the surface of the original during feeding-reading. In Japanese Patent Application Laid-Open No. 2013-236286, in the fixed original reading mode, only the second reflection plate remote from the platen is moved integrally with a scanning unit (carriage), to prevent contact with the integrally moving carriage due to deformation of the platen unit caused by the weight of a book or the like.
However, even if the reflection plate is provided in the clearance between the light source unit and the platen to increase the amount of illumination onto the platen during feeding-reading as described in Japanese Patent Application Laid-Open No. 2013-236286, the effect is small for the case with a small light beam leakage at the position.